For many years, roofs were of the built-up type, in which multiple layers of material, including a felt material soaked with bitumen, were used. Gravel was placed over this built-up roof, as a ballast to hold it down against being lifted by the wind. The built-up roof included bitumen as a material which would be impervious to penetration by moisture, such as rain.
In more recent times, an alternate roofing system has been employed, which is designated as "single-ply". The single-ply roofing system includes the application of a membrane of a suitable elastomeric material over a substrate. The substrate may be either rigid or non-rigid. Rigid substrates include concrete, sheet metal, as well as various types of insulation boards. Insulation boards include fiberboard, perlite board, fiberglass with binder, urethane, urethane with composite of fiberboard, perlite or fiberglass, polystyrene, cellular glass and cork board. Non-rigid roofing materials include batt or blanket types of insulation,, which is compressible, as for example, by a fastener which penetrates the insulation as well as a membrane which is placed over the installation.
The membrane may be made of various selected materials, including chlorinated polyethylene, ethylene propylene diene monomer, chlorosulfonated polyethylene, modified bitumen, neoprene, polyisobutylene and polyvinyl chloride. These materials are generally produced in sheets which are transported in rolls, which are often sold in widths of from about 3 feet to as much as approximately 40 feet, and the length may be as much as 125 feet.
The membrane must not only be waterproof, but must be prevented from being lifted by wind forces. A waterproof membrane construction is achieved by applying the membrane in sheets or strips, lapping one over the other, and providing a joint at the overlap, which is waterproof and moisture proof. Also, of course, flashing in one form or other is utilized at the edges of the membrane, at pipes, etc.
The adherence of the membrane to the roof is achieved in several different ways. One is a loose-laid ballast system, in which small stones are placed over the membrane, to hold it down. Another is the partially attached system, in which fasteners penetrate the membrane and are secured to the substrate, such as the rigid insulation boards above-mentioned. The partially-attached single-ply system may be utilized with either strips or various so called "point attachment" constructions. There is also a totally adhered system, in which the entire undersurface of the membrane is adhered by a suitable adhesive to the substrate, as well as a so called protected membrane roof, which provides for insulation over the membrane.
In the partially-attached single-ply systems, there are several problems which must be overcome. In both of the "point attachment" constructions, in which a plate or disc is over the membrane and has a linear fastener passed through it and through the membrane into the underlying roof structure, herein called the roof substrate, there is used only a single fastener for each such plate or disc. In areas where there are strong wind forces, this neccessitates the utilization of a higher concentration of the discs or plates, and the construction must have suitable protection against the entry of water into the building structure by finding a passage-way along the fastener and through the penetrated membrane. Similarly in the strip attachment, to provide for suitable security in high wind areas, the strips must be more closely concentrated, and suitable provision must be made to insure against water leakage through the membrane where it is penetrated by the linear fasteners.
While various partially attached systems, as above described, have been installed in recent times, and have proven to be satisfactory, improvement is needed to achieve satisfactory membrane hold-down in high wind areas, without increasing the concentration of the discs, or strips, and the attendant expenses. In addition, improvement is needed in providing a system in which the membrane is not penetrated, so as to avoid the possibility that precautions taken to prevent water leakage along the fastener and through the penetrated membrane are not successful.